Area detector systems are invaluable tools for experimentation and research in a wide variety of scientific and medical endeavors. Over the years, these detectors have been used as analytical and diagnostic devices in such diverse fields as crystallography, medical radiography, electron microscopy, biophysics, and astronomy. Earlier area detection devices were of two general types: (1) the multiwire proportional counters (such as described in Bateman et al, Nuc. Inst. Meth. Phvs. Res. A259: 506-520 (1987)) and (2) TV detectors (see, e.g., Kalata, Methods in Enzymology 114: 486-510 (1985)). Although devices of these two types are still used successfully in particular applications, they suffer from several drawbacks. In particular, these devices generally are limited in active area and spatial resolution, experience high levels of spatial distortion and nonuniformity of response, and require a prolonged exposure to X-rays in order to develop a satisfactory picture. In cases where an instantaneous image of a rapidly deteriorating sample is required, these prior art systems are not rapid enough to provide near real time images, and thus are not suitable for these applications. One example of where almost instantaneous imaging is necessary is the field of protein crystallography. Protein single crystals are grown so that the three dimensional structure of the protein can be determined by X-ray diffraction. Typically, these grown protein crystals deteriorate very rapidly with both time and handling, and the specific details of the protein structure will be lost if an X-ray pattern from the crystals cannot be obtained within a short period after their formation. It is thus necessary to develop a system for area detection which has rapid data acquisition, and which can thus provide near real time imaging capabilities for X-ray patterns.
A recent discovery of the unique properties of particular phosphor-containing films has enabled new developments in X-ray and UV-sensitive area detection devices. It has been found that a plate containing barium fluorohalide (BaFX:Eu) crystals will absorb a particular fraction of incident X-ray or UV radiation by "trapping" an electron in a halogen ion vacancy or "F-center". Electrons so trapped will normally be stored at a half life of approximately 10 hours. However, if the film is irradiated with visible light, the electrons trapped in the F-center will be liberated to the conduction band leading to the formation of Eu.sup.+2 ions in an excited state. These excited ions then relax to give off luminescence proportional in intensity to the X-ray or UV irradiation originally absorbed. It is thus possible using such phosphor-containing films to create a stored or "latent image" on the film which can almost immediately be "dumped" or transmitted by subsequent illumination with light or other electromagnetic wave at an appropriate wavelength. After such "dumping" of the image, the phosphor film returns to its original state and can be reused for further X-ray imaging.
One device incorporating such a phosphor film has been constructed, and is described in Miyahara et al, Nuc. Inst. Meth. Phvs. Res. A246: 572-578 (1986). This device essentially consists of a BaFBr:Eu.sup.2+ phosphor screen imaging plate, a laser beam reflected by a scanning mirror, a light guide, which collects the photostimulated luminescent radiation, and a photomultiplier tube into which the collected light is channeled. In this setup, a He-Ne laser beam emitting light at 632.8 nm is used to illuminate the film, which luminesces at around 390 nm in response to the laser. This system, however, also suffers from certain drawbacks such as its ability to only scan line by line, as opposed to additionally being able to scan an entire area at once, and its use of complex photomultiplier tubes which limit the resolution and reliability of the system. Further, the complex and sensitive components necessary for this system limit the ability to make the system compact and durable, as would be required for X-ray detection devices used in protein crystallization studies carried out in space or in other zero-gravity environments. What is desired, therefore, is an X-ray or UV-sensitive detection device which can be made from simple, commercially available components, which can successfully employ phosphor-containing films to create near real time images of rapidly deteriorating sample with high spatial resolution, and which can also be made into a compact and rugged unit suitable for carrying out X-ray imaging under a variety of conditions.